Is It Possible to Have Straight Invisalign Trays and Still Crooked Teeth?

in the end of the treatment? I have just started Inv treatment. I can see my last trays look very straight and I expect that only straight teeth to be able to fit in them and in the end to be as straight exaclty as the trays. If so why then it's very common to get refinements? Is it because in spite of straight trays the teeth are still not so straight as supposed or it is because the teeth are straight as they should be but the patient is still not satisfied with the real live result?

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